NRA Thames 254 National Rivers Authority Thames Region TR44 River Thames (Eynsham to Benson) and Ock Catchment Review October 1994 NRA Thames Region Document for INTERNAL CIRCULATION only National River Authority Thames Region Catchment Planning - West River Thames (Eynsham to Benson) and Ock Catchment Review October 1994 River Thames (Eynsham to Benson) and Ock - Catchment Review CONTENTS Page 1. INTRODUCTION 2. THE CURRENT STATUS OF THE WATER ENVIRONMENT Overview 2 Geology and Topography 2 Hydrology 2 Water Resources 5 Water Quality 9 Pollution Control 14 Consented Discharges 15 * Flood Defence 18 Fisheries 18 Conservation 19 Landscape 21 Recreation 23 Navigation 26 Land Use Planning Context 29 Minerals 31 P2J73/ i River Thames (Eynsham to Benson) and Ock - Catchment Review Page 3. CATCHMENT ISSUES 34 South West Oxfordshire Reservoir Proposal 34 Ground water Pollution 35 River Levels & Flows 35 Habitat Degradation 35 Wolvercote Pit 36 Eutrophication of the Thames 36 River Thames : Seacourt Stream Relationship 36 The River Thames Through Oxford 37 Oxford Structures Study 37 Oxford Sewage Treatment Works 37 Kidlington Sewage Treatment Works 38 Oxford Sewers 38 Development Pressure 38 Navigation Issues 39 Landscape Issues 39 Recreation Issues 39 Wiltshire Berkshire Canal 40 Summary of Key Issues 41 4. CATCHMENT ACTIONS 43 5. CONCLUSIONS AND RECOMMENDATIONS 51 P2573/ i i River Thames (Eynsham to Benson) and Ock - Catchment Review LIST OF TABLES Page 2.1 Details of Licensed Ground/Surface Water Abstractions of Greater than lML/day 9 2.2 RQOs, NWC Classification, RE Objectives and GQAs for the Study Area 12 2.3 Consented Discharges and Percentage Compliance 15 2.4 Discharge Consents of Volumes Greater than 10,000m3/day 16 2.5 Pedestrian Counts: Abingdon 25 2.6 Pedestrian Counts: Thames Towpath at Kennington 25 2.7 Thames Lock Traffic (Eynsham to Benson) 26 4.1 Summary of Recent NRA Activity (Post September 1989) 44 4.2 Summary of NRA Activity (1993/94) 46 4.3 Summary of Planned NRA Activity (1994/95 and Beyond) 48 5.1 Summary of Recommendations 52 F2J73/ iii River Thames (Eynsham to Benson) and Ock - Catchment Review LIST OF FIGURES Page 1 The Study Area - Key Features 3 2 Geology 4 3a-c Hydrology 6 4 Water Resources 10 5 Water Quality (GQA) 11 6 Reported Pollution Incidents 1993 14 7 Biological Water Quality 17 8 Nature Conservation 20 9 Planning Policy 22 10 Recreation 24 11 Minerals 32 12 Catchment Issues 42 Please Note: You will notice that the grid references used on the maps above differ from those given in the text through the use of ’SU ’ in the latter. For conversion, the first digit of the Easting and Northing can be replaced by the relevant letter as follows; s u s o 4 1 3 2 5 P S T . 4 2 3 1 eg OS system SU390271 is equivalent to 439127 (within the grid coordinates of 430000 and 120000). The use of grid letters to divide up Great Britain was devised by Ordnance Survey to ease location. For greater accuracy six figure grid references are then utilised. Alternatively, a purely numerical system can be adopted ie digitally for GIS purposes. P2573/ iv River Thames (Eynsham to Benson) and Ock - Catchment Review 1. INTRODUCTION 1.1 The National Rivers Authority (NRA) was established by the Water Act 1989. The NRA has defined its role in the following “mission statement’7: * We will protect and improve the water environment by the effective management of water resources and by substantial reductions in pollution. We will aim to provide effective defence for people and property against flooding from rivers and the sea. In discharging our duties we will operate openly and balance the interests of all who benefit from and use rivers, ground waters, estuaries and coastal waters. ’ 1.2 In order to effectively manage the water environment and sustain it for the future, the NRA has adopted the principle of Catchment Management Planning. This entails the preparation of Catchment Management Plans (CMP) for each natural river catchment within England and Wales. Through data evaluation, issues analysis, external liaison and consultation, the CMP provides a vehicle to focus attention on the water environment. The process involves all interested parties, in planning for the future well being of the catchment and establishes an integrated plan of action for managing the catchment over a period of five years, after which it is reviewed. 1.3 However, as a precursor to the commissioning of the Catchment Management Plans, brief and succinct Catchment Reviews such as this are being drafted which will: a) provide a concise summary of the current status of the water environment; b) make full use of the knowledge of internal staff and their assessments of the value of the catchment to people and wildlife; c) provide a focus for integrating on-going NRA functional activities; d) promote, region-wide awareness of issues and opportunities and priorities for action; e) facilitate the prioritization and production of Catchment Management Plans. 1.4 The following review will provide a summary of catchment statistics, issues, current and future proposed NRA activity in order to achieve a broad awareness of potential opportunities and constraints. The document will also form the basis of the full Catchment Management Plan which will provide the focus for those concerned with the future well­ being of the water environment of the area; - - ■ " " F2J73/ 1 River Thames (Eynsham to Benson) and Ock - Catchment Review 2. THE CURRENT STATUS OF THE WATER ENVIRONMENT OVERVIEW 2.1 The Catchment Review study area covers the Ock catchment and the section of the River Thames from Eynsham Lock to Benson Lock as illustrated in Figure 1. The study area covers approximately 544 km2 and is predominantly rural in character, with the two significant urban areas being Oxford and Abingdon. The study area has a population of approximately 189,000. Oxford has a population of approximately 127,000, Abingdon 31,000 and Didcot 16,000 (1991 figures). GEOLOGY AND TOPOGRAPHY 2.2 The Ock catchment is characterised by Gault and Kimmeridge clays, which are easily erodible and therefore promote lowland development. To the south the clays are overlain by Chalk rising up to form the rolling landscape of the Berkshire Downs. The Downs form an upland ridge with an average height of 210m AOD along the southern edge of the study area, rising up to a maximum height of 240m AOD at White Horse Hill. 2.3 To the north, the Corallian Series largely comprising sand and limestone beds forms a small discontinuous scarp overlain by the Lower Greensand Formation (Faringdon Sponge Beds). To the north east the land dips once more to expose the lowland Oxford Clays. 2.4 The River Ock rises at Little Coxwell and flows over the Corallian gaining flow from a number of spring fed tributaries. Downstream of Garford to its confluence with the River Thames the river flows over Kimmeridge Clays and Terrace Gravels overlying the clay. Along the Thames valley, the underlying geology is masked by Pleistocene alluvium and gravels. Figure 2 shows the solid geology of the study area. HYDROLOGY 2.5 The Ock rises at Little Coxwell (SU 280935) and flows eastward for 38km to meet the Thames at Abingdon (SU 496967). The seven major tributaries of the Ock are: the Childrey Brook, the Bagpuize Brook, the Marcham Brook, the Sandford Brook, the Land Brook, the Stutfield Brook and the Letcombe Brook. In their upper reaches many of these tributaries have been managed for agricultural purposes and are little more than field drains in narrow entrenched channels, the majority of which do not flow all year round. The Letcombe Brook however remains a pristine chalk stream in its upper lengths. P2573/ 2 Thames (Eynsham to Benson) & Ock Catchment Review: Key Features □ CMP Boundary Sub - Catchment Boundar y [ I Urban Areas Main River River Thames Lock Motorway 'A' Road Railway Principal Station Scale > 10km NRA National Ri\trs Authority Thames Region Crown Copyright Automobifc Association twjSMtw N Figure 2 Thames (Eynsham to Benson) & Ock Catchment Review: Solid Geology 210000 □ CMP Boundary River Thames Mam River Middle Chalk Lower Chalk Upper Green sand Gault Lower Greensand Portland □ Beds ■ Kimmendge Clay □ Corallian Oxford Clay □ Combrash n Forest Marble Scale 10km NRA National Rnvrs Authority Thames Region © Crown Copyright © AulomoOSs Association 8JW06 River Thames (Eynsham to Benson) and Ock - Catchment Review 2.6 Many of the smaller watercourses in this catchment have in the past few years suffered from low summer base flows and drought conditions. 2.7 The Oxford Canal runs through part of the study area. The canal was constructed in the eighteenth century to form a link between the Coventry Canal and the River Thames and to provide a means of transporting coal. Jurisdiction over water quality, recreation and fisheries is shared between NRA Thames Region and the British Waterways, with navigation and engineering on the canal being the sole responsibility of British Waterways. (The route of the old Wiltshire and Berkshire Canal also runs through the catchment area.) 2.8 Figures 3a - 3c show hydrographs for the River Thames at Eynsham and Days Lock and for the River Ock at Abingdon respectively. The hydrographs for the River Thames show flow increases between Eynsham and Days weir, but the flow pattern is constant. Tributaries of the Thames along this reach include the Evenlode and Cherwell as well as the Ock. The Ock hydrograph shows the flashy nature of the watercourse with 1991 and 1992 being particularly dry years. WATER RESOURCES 2.9 A proportion of the rainfall falling on the catchment is subsequently lost as evaporation or transpiration. The remainder, termed the ’effective rainfall’ is the total water resource available to the catchment in the form of either surface run-off or ground water recharge.